The invention relates to sheet inverter and stacking apparatus and in particular to the offsetting and accurate registration of sheets produced from automatic printing machines at high speeds.
In an electrostaticgraphic reproducing apparatus commonly in use today, a photoconductive insulating member is typically charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image areas contained within the usual document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with developing powder referred to in the art as toner. Most development systems employ a developer material which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development the toner particles are attracted from the carrier particles by the charge pattern of the image areas on the photoconductive insulating area to form a powder image on the photoconductive areas. This image may subsequently be transferred to a support surface such as copy paper to which it may be permanently affixed by heating or by the application of pressure. Following transfer of the toner image to a support surface, the photoconductive insulating member is cleaned of any residual toner that may remain thereon in preparation for the next imaging cycle. Alternatively, the electrostatic latent image may be generated from information electronically stored or generated in digital form which afterwards may be converted to alphanumeric images by image generation, electronics and optics. In such a printer application a beam of light such as a laser beam may be used to selectively discharge the photoconductor.
Commercial applications of this process have taken various forms. One in particular is that of the printer application referred to above wherein finished sets of prints are collected such that the registered edge of successive sets are offset slightly each from the other.